Granulocyte Colony Stimulating Factor Enhances Reward Learning through Potentiation of Mesolimbic Dopamine System Function.

Deficits in motivation and cognition are hallmark symptoms of multiple psychiatric diseases. These symptoms are disruptive to quality of life and often do not improve with available medications. In recent years there has been increased interest in the role of the immune system in neuropsychiatric illness, but to date no immune-related treatment strategies have come to fruition. The cytokine granulocyte-colony stimulating factor (G-CSF) is known to have trophic and neuroprotective properties in the brain, and we recently identified it as a modulator of neuronal and behavioral plasticity. By combining operant tasks that assess discrete aspects of motivated behavior and decision-making in male mice and rats with subsecond dopamine monitoring via fast-scan cyclic voltammetry, we defined the role of G-CSF in these processes as well as the neural mechanism by which it modulates dopamine function to exert these effects. G-CSF enhanced motivation for sucrose as well as cognitive flexibility as measured by reversal learning. These behavioral outcomes were driven by mesolimbic dopamine system plasticity, as systemically administered G-CSF increased evoked dopamine release in the nucleus accumbens independent of clearance mechanisms. Importantly, sustained increases in G-CSF were required for these effects as acute exposure did not enhance behavioral outcomes and decreased dopamine release. These effects seem to be a result of the ability of G-CSF to alter local inflammatory signaling cascades, particularly tumor necrosis factor α. Together, these data show G-CSF as a potent modulator of the mesolimbic dopamine circuit and its ability to appropriately attend to salient stimuli.SIGNIFICANCE STATEMENT Emerging evidence has highlighted the importance of the immune system in psychiatric diseases states. However, the effects of peripheral cytokines on motivation and cognitive function are largely unknown. Here, we report that granulocyte-colony stimulating factor (G-CSF), a pleiotropic cytokine with known trophic and neuroprotective properties in the brain, acts directly on dopaminergic circuits to enhance their function. These changes in dopaminergic dynamics enhance reward learning and motivation for natural stimuli. Together, these results suggest that targeting immune factors may provide a new avenue for therapeutic intervention in the multiple psychiatric disorders that are characterized by motivational and cognitive deficits.

Cafeteria diet induces neuroplastic modifications in the nucleus accumbens mediated by microglia activation.

High-palatable and caloric foods are widely overconsumed due to hedonic mechanisms that prevail over caloric necessities leading to overeating and overweight. The nucleus accumbens (NAc) is a key brain area modulating the reinforcing effects of palatable foods and is crucially involved in the development of eating disorders. We describe that prolonged exposure to high-caloric chocolate cafeteria diet leads to overeating and overweight in mice. NAc functionality was altered in these mice, presenting structural plasticity modifications in medium spiny neurons, increased expression of neuroinflammatory factors and activated microglia, and abnormal responses after amphetamine-induced hyperlocomotion. Chronic inactivation of microglia normalized these neurobiological and behavioural alterations exclusively in mice exposed to cafeteria diet. Our data suggest that prolonged exposure to cafeteria diet produces neuroplastic and functional changes in the NAc that can modify feeding behaviour. Microglia activation and neuroinflammation play an important role in the development of these neurobiological alterations.

Chronic ethanol consumption: role of TLR3/TRIF-dependent signaling.

Chronic ethanol consumption stimulates neuroimmune signaling in the brain, and Toll-like receptor (TLR) activation plays a key role in ethanol-induced inflammation. However, it is unknown which of the TLR signaling pathways, the myeloid differentiation primary response gene 88 (MyD88) dependent or the TIR-domain-containing adapter-inducing interferon-ß (TRIF) dependent, is activated in response to chronic ethanol. We used voluntary (every-other-day) chronic ethanol consumption in adult C57BL/6J mice and measured expression of TLRs and their signaling molecules immediately following consumption and 24 hours after removing alcohol. We focused on the prefrontal cortex where neuroimmune changes are the most robust and also investigated the nucleus accumbens and amygdala. Tlr mRNA and components of the TRIF-dependent pathway (mRNA and protein) were increased in the prefrontal cortex 24 hours after ethanol and Cxcl10 expression increased 0 hour after ethanol. Expression of Tlr3 and TRIF-related components increased in the nucleus accumbens, but slightly decreased in the amygdala. In addition, we demonstrate that the IKKε/TBK1 inhibitor Amlexanox decreases immune activation of TRIF-dependent pathway in the brain and reduces ethanol consumption, suggesting the TRIF-dependent pathway regulates drinking. Our results support the importance of TLR3 and the TRIF-dependent pathway in ethanol-induced neuroimmune signaling and suggest that this pathway could be a target in the treatment of alcohol use disorders.

Adolescent morphine exposure affects long-term microglial function and later-life relapse liability in a model of addiction.

Adolescence in humans represents a unique developmental time point associated with increased risk-taking behavior and experimentation with drugs of abuse. We hypothesized that exposure to drugs of abuse during adolescence may increase the risk of addiction in adulthood. To test this, rats were treated with a subchronic regimen of morphine or saline in adolescence, and their preference for morphine was examined using conditioned place preference (CPP) and drug-induced reinstatement in adulthood. The initial preference for morphine did not differ between groups; however, rats treated with morphine during adolescence showed robust reinstatement of morphine CPP after drug re-exposure in adulthood. This effect was not seen in rats pretreated with a subchronic regimen of morphine as adults, suggesting that exposure to morphine specifically during adolescence increases the risk of relapse to drug-seeking behavior in adulthood. We have previously established a role for microglia, the immune cells of the brain, and immune molecules in the risk of drug-induced reinstatement of morphine CPP. Thus, we examined the role of microglia within the nucleus accumbens of these rats and determined that rats exposed to morphine during adolescence had a significant increase in Toll-like receptor 4 (TLR4) mRNA and protein expression specifically on microglia. Morphine binds to TLR4 directly, and this increase in TLR4 was associated with exaggerated morphine-induced TLR4 signaling and microglial activation in rats previously exposed to morphine during adolescence. These data suggest that long-term changes in microglial function, caused by adolescent morphine exposure, alter the risk of drug-induced reinstatement in adulthood.

Sensitization to amphetamine occurs simultaneously at immune level and in met-enkephalin of the nucleus accumbens and spleen: an involved NMDA glutamatergic mechanism.

Administration of psychostimulants can elicit a sensitized response to the stimulating and reinforcing properties of the drugs, although there is scarce information regarding their effects at immune level. We previously demonstrated that an acute exposure to amphetamine (5 mg/kg, i.p.) induced an inhibitory effect on the splenic T-cell proliferative response, along with an increase in met-enkephalin at limbic and immune levels, 4 days following drug administration. In this study, we evaluated the amphetamine-induced effects at weeks one and three after the same single dose treatment (5 mg/kg, i.p.) on the lymphoproliferative response and on the met-enkephalin in the nucleus accumbens (NAc), prefrontal cortex (PfC), spleen and thymus. It was demonstrated that these effects disappeared completely after three weeks, although re-exposure to an amphetamine challenge induced the expression of sensitization to the effects of amphetamine on the lymphoproliferative response and on the met-enkephalin from NAc, spleen and thymus, but not in the PfC. Pre-treatment with MK-801 (0.1 mg/kg, i.p.), an N-methyl-d-aspartate (NMDA) glutamatergic receptor antagonist, blocked the effects of a single amphetamine exposure on the lymphoproliferative response and on met-enkephalin in the NAc and spleen. Furthermore, the NMDA receptor antagonist administered prior to amphetamine challenge also blocked the expression of sensitization in both parameters evaluated. These findings show a long-lasting amphetamine-induced sensitization phenomenon at the immune level in a parallel way to that occurring in the limbic and immune enkephalineric system. A glutamate mechanism is implied in the long-term amphetamine-induced effects at immune level and in the met-enkephalin from NAc and spleen.

Changes in hyporesponsiveness to acute amphetamine and age differences in tyrosine hydroxylase immunoreactivity in the brain over adolescence in male and female rats.

We investigated hyposensitivity after amphetamine in early (postnatal Day 30; P30) and late (P45) adolescent rats compared to adults (P70) in experiment 1. Locomotor activity was measured for 1 hr after the first (acute) and second (24 hr later) injection of amphetamine (0.5 or 1.5 mg/kg). P30 and P45 rats were transiently hypoactive compared to adults, as indicated by reduced locomotor activity after acute amphetamine and enhanced activity after the second injection in adolescents only. In experiment 2, ovariectomy did not alter locomotor activity during habituation at any age compared to intact rats, and, as for intact adolescents, ovariectomized adolescents continued to be less active after amphetamine than adults, suggesting gonadal immaturity alone cannot account for age differences in experiment 1. However, ovariectomy attenuated the increase in activity after the second treatment. In experiment 3 involving untreated rats, tyrosine hydroxylase immunoreactivity was reduced in P30, P40, and P50 compared to P90 rats in the nucleus accumbens core and the medial prefrontal cortex. Thus, adolescents may have an increased threshold of behavioral activation that can be overcome with either a higher dose or with repeated amphetamine treatment, and may be related to changes in the dopamine system over development.

Opioid-Induced Hyperalgesia Is Associated with Dysregulation of Circadian Rhythm and Adaptive Immune Pathways in the Mouse Trigeminal Ganglia and Nucleus Accumbens.

The benefits of opioid-based treatments to mitigate chronic pain can be hindered by the side effects of opioid-induced hyperalgesia (OIH) that can lead to higher consumption and risk of addiction. The present study advances the understanding of the molecular mechanisms associated with OIH by comparing mice presenting OIH symptoms in response to chronic morphine exposure (OIH treatment) relative to control mice (CON treatment). Using RNA-Seq profiles, gene networks were inferred in the trigeminal ganglia (TG), a central nervous system region associated with pain signaling, and in the nucleus accumbens (NAc), a region associated with reward dependency. The biological process of nucleic acid processing was over-represented among the 122 genes that exhibited a region-dependent treatment effect. Within the 187 genes that exhibited a region-independent treatment effect, circadian rhythm processes were enriched among the genes over-expressed in OIH relative to CON mice. This enrichment was supported by the differential expression of the period circadian clock 2 and 3 genes (Per2 and Per3). Transcriptional regulators in the PAR bZip family that are influenced by the circadian clock and that modulate neurotransmission associated with pain and drug addiction were also over-expressed in OIH relative to CON mice. Also notable was the under-expression in OIH relative to CON mice of the Toll-like receptor, nuclear factor-kappa beta, and interferon gamma genes and enrichment of the adaptive immune processes. The results from the present study offer insights to advance the effective use of opioids for pain management while minimizing hyperalgesia.

Prenatal immune challenge induces behavioral deficits, neuronal remodeling, and increases brain nitric oxide and zinc levels in the male rat offspring.

Schizophrenia is a severe mental disorder with numerous etiological susceptibilities. Maternal infection is a key risk factor for schizophrenia. Prenatal lipopolysaccharide (LPS) infection stimulates cytokine production that affects brain development. In the present study, we aimed to investigate the effect of prenatal LPS injection at gestational day (GD) 14-16 on behavioral paradigms, and neuronal morphology in the prefrontal cortex (PFC), basolateral amygdala (BLA), nucleus accumbens (NAcc) and ventral hippocampus (VH) at two critical ages of development: pre-pubertal (postnatal day 35, PD35) and post-pubertal (PD60) age in male rats. We also evaluated the effects of LPS on nitric oxide (NO) and zinc (Zn) levels in seven brain areas (PFC, VH, amygdala, brainstem, striatum and dorsal hippocampus) at PD35 and PD60. LPS induced hyperlocomotion in a novel environment and reduced social contact as well as increased the levels of NO and Zn in the PFC, brainstem and amygdala as observed in other animal models of schizophrenia-related behavior. Furthermore, we found that LPS-treated rats presented post-pubertal neuronal hypertrophy in the PFC and BLA and decreased spine density in the NAcc. The neuronal morphology of neurons in the VH in LPS-treated rats remained unaltered. Interestingly, the anxiogenic-related behavior correlated with neuronal hypertrophy observed in the BLA. Our findings suggest that the behavioral and neural modifications observed in our model could be mediated by the long-lasting alterations in Zn and NO levels in the brain.

How does immune challenge inhibit ingestion of palatable food? Evidence that systemic lipopolysaccharide treatment modulates key nodal points of feeding neurocircuitry.

Immune challenge induces behavioral changes including reduced ingestion of palatable food. Multiple pathways likely contribute to this effect, including viscerosensory pathways controlling hypothalamic feeding circuits or by influence on "reward" circuitry previously established to control ingestive behavior. To investigate whether the effects of immune challenge may influence this network, we compared brain activation patterns in animals trained to drink a palatable sweetened milk solution and treated systemically with either the immune stimulant lipopolysaccharide (LPS) or saline. Brain sections were processed for localization of the activation marker c-Fos in neurons of regions implicated in regulation of feeding behavior. Sweetened milk ingestion was associated with increased numbers of c-Fos positive neurons in the caudal core and shell of the nucleus accumbens (NAc), the paraventricular thalamus (PVT), central nucleus of the amygdala (CEA), the basal lateral amygdala (BLA), in orexin-A containing neurons of the lateral hypothalamus (LH), and in cocaine and amphetamine regulated transcript (CART) neurons of the arcuate hypothalamus. In LPS-treated animals sweetened milk consumption was significantly reduced, as was c-Fos induction in the hypothalamic orexin-A and CART neurons, and in the BLA. In addition, induction of c-Fos in the rostral regions of the NAc, the PVT, and CEA was increased following LPS treatment, compared to controls. The findings from this study point to a network of brain regions (LH, PVT, NAc, and BLA) previously implicated in the modulation of feeding behavior, reward, and arousal that may also contribute to neural substrates involved in the reorganization of behavioral priorities that occurs during sickness.

Microglial dopamine receptor elimination defines sex-specific nucleus accumbens development and social behavior in adolescent rats.

Adolescence is a developmental period in which the mesolimbic dopaminergic "reward" circuitry of the brain, including the nucleus accumbens (NAc), undergoes significant plasticity. Dopamine D1 receptors (D1rs) in the NAc are critical for social behavior, but how these receptors are regulated during adolescence is not well understood. In this report, we demonstrate that microglia and complement-mediated phagocytic activity shapes NAc development by eliminating D1rs in male, but not female rats, during adolescence. Moreover, immune-mediated elimination of D1rs is required for natural developmental changes in male social play behavior. These data demonstrate for the first time that microglia and complement-mediated immune signaling (i) participate in adolescent brain development in a sex-specific manner, and (ii) are causally implicated in developmental changes in behavior. These data have broad implications for understanding the adolescent critical period of development, the molecular mechanisms underlying social behavior, and sex differences in brain structure and function.

Involvement of dopamine D1 and D2 receptors in the rat nucleus accumbens in immunostimulation.

Analysis of the nature of changes in the immune response in operated Wistar rats showed that electrolytic lesioning of the nucleus accumbens, the site of the greatest density of dopamine D1 and D2 receptors, led to suppression of the immune response in animals immunized with sheep erythrocytes. Administration of SKF 38393 (20 mg/kg) and quinpirol (1 mg/kg), selective agonists of dopamine D1 and D2 receptors respectively, to sham-operated rats induced significant increases in immune responses. However, no immunostimulation was seen on administration of the selective dopamine D2 agonist quinpirol to animals with lesions to the nucleus accumbens as compared with controls. At the same time, treatment of animals with nucleus accumbens lesions using the dopamine D1 receptor agonist SKF 38393 had no effect on the immune response as compared with that in sham-operated animals given the D1 receptor agonist. These data provide evidence that dopamine D2 receptors in the nucleus accumbens have a role in the mechanisms of immunostimulation, though D2 receptors in other brain structures may also make some contribution to this process; D1 receptors in the nucleus accumbens make no significant contribution to controlling the immune response.

Suppression of natural killer cell activity by morphine is mediated by the nucleus accumbens shell.

Despite a wealth of data indicating that morphine modulates immune status by acting at mu-opioid receptors in the brain, there is little known about how the opioid system interacts with other neurotransmitter systems to modulate specific immune parameters. The aim of the present study was to investigate whether dopaminergic projections to the nucleus accumbens are involved in morphine-induced suppression of splenic natural killer (NK) cell activity. The results indicate that administration of the dopamine D1 antagonist SCH-23390 into the nucleus accumbens shell, but not core, blocked morphine's suppressive effect on NK activity in male Lewis rats. In support of these findings, the effect of morphine was also prevented by intra-accumbens microinfusions of the dopaminergic immunotoxin anti-DAT-saporin. Additionally, administration of the D1 agonist SKF-38393 into the nucleus accumbens shell produced reductions in splenic NK activity comparable to morphine, suggesting a critical role for D1 receptors in the modulation of NK activity. Collectively, these findings demonstrate that dopaminergic inputs to the nucleus accumbens are critically involved in opioid-induced immunosuppression and suggest that opioid-induced increases in D1 receptor activation may have adverse consequences on immune status.

Neuropeptide Y Y1 receptors mediate morphine-induced reductions of natural killer cell activity.

Morphine suppresses a number of immune parameters, such as natural killer (NK) cell activity and lymphocyte proliferation, by acting through mu-opioid receptors in the central nervous system. Prior studies have implicated the sympathetic nervous system in mediating the immunomodulatory effects of acute morphine treatment. However, the peripheral mechanism whereby morphine inhibits NK cell activity is not fully understood. The aim of the present study was to investigate the role of the sympathetic transmitter neuropeptide Y (NPY) in mediating morphine-induced immune alterations. The results showed that administration of the selective NPY Y1 receptor antagonist BIBP3226 blocked morphine's effect on splenic NK activity but did not attenuate the suppression splenocyte proliferative responses to Con-A or LPS. Furthermore, intravenous NPY administration produced a dose-dependent inhibition of splenic NK activity but did not suppress lymphocyte proliferation. Recent studies from our laboratory have demonstrated that morphine modulates NK activity through a central mechanism that requires the activation of dopamine D1 receptors in the nucleus accumbens. Results from the present study showed that microinjection of the D1 receptor agonist SKF-38393 into the nucleus accumbens shell induced a suppression of NK activity that was reversed by BIBP3226. Collectively, these findings demonstrate that NPY Y1 receptors mediate morphine's suppressive effect on NK activity and further suggest that opioid-induced increases in nucleus accumbens D1 receptor activation inhibit splenic NK activity via NPY released from the sympathetic nervous system.

Ultrastructural characteristics of enkephalin-immunoreactive boutons and their postsynaptic targets in the shell and core of the nucleus accumbens of the rat.

The present study compared the ultrastructural morphology of enkephalin-immunoreactive boutons and their postsynaptic targets in different territories of the nucleus accumbens in the rat. The synaptic bouton profiles were identified by antibodies directed against [leu5]enkephalin. Ninety-five percent of the synaptic contacts were symmetric in configuration and the remaining 5% were asymmetric. Axosomatic contacts comprised 6% of all enkephalin-immunoreactive junctions and were distributed equally in all parts of the nucleus. Most (76%) synaptic terminals contacted dendrites but they contacted proportionally fewer dendrites in the shell (71%) than in the core (78%). Moreover, enkephalin-immunoreactive synaptic boutons in the shell (19%) and caudal enkephalin-rich areas (17%) of the core contacted twice as many spines than in the remaining parts of the core (8.5%). In the core, long pallidum-like dendrites were occasionally found ensheathed in enkephalin-immunoreactive terminal boutons. We conclude that the differential arrangement of enkephalinergic contacts in the shell and core could have important functional consequences, especially when considered in relation to other known morphological and neurochemical differences between these regions.

D1 and D2 dopamine receptors differentially increase Fos-like immunoreactivity in accumbal projections to the ventral pallidum and midbrain.

Alterations in dopaminergic neurotransmission have profound effects on neuronal expression of the putative activity marker, Fos, in both the dorsal and ventral striatum. Stimulants such as D-amphetamine and cocaine increase Fos-like immunoreactivity by enhancing the activation of D1 dopamine receptors. In contrast, neuroleptics such as haloperidol and raclopride increase Fos-like immunoreactivity by blocking striatal D2 dopamine receptors. In the dorsal striatum, D1 receptor stimulation elevates Fos-like immunoreactivity predominantly in neurons projecting to the midbrain (substantia nigra), whereas D2 receptor antagonism enhances Fos-like immunoreactivity principally in neurons projecting to the pallidum (globus pallidus). These findings are consistent with the proposal that D1 receptors are located chiefly on striatonigral neurons, whereas D2 receptors reside mainly on striatopallidal neurons. Since the nucleus accumbens (largest component of the ventral striatum) also sends projections to the midbrain (ventral tegmental area and substantia nigra) and pallidum (ventral pallidum), the present study utilized retrograde tract-tracing techniques to determine if there was a similar segregation of D1 agonist- and D2 antagonist-induced Fos-like immunoreactivity in these accumbal projections. In addition, we examined whether these relationships were the same in the core and shell regions of the nucleus accumbens. Like the dorsal striatum, D1 agonists (D-amphetamine and CY 208-243), but not D2 antagonists (haloperidol and clozapine), increased Fos-like immunoreactivity in accumbal neurons projecting to the midbrain (ventral tegmental area and substantia nigra). Also like the dorsal striatum, D2 antagonist-induced Fos-like immunoreactivity was located preferentially in accumbal neurons projecting to the pallidum (ventral pallidum). However, unlike the dorsal striatum, where the vast majority of neurons which display D1 agonist-induced Fos-like immunoreactivity project to the midbrain, nearly 50% of those neurons in the nucleus accumbens which were Fos-immunoreactive after D-amphetamine or CY 208-243 projected to the ventral pallidum. Thus, a similar number of accumbal neurons which expressed D1 agonist-induced Fos-like immunoreactivity were retrogradely labelled from the midbrain and ventral pallidum. Accumbal projections to the midbrain and ventral pallidum were retrogradely labelled with different retrograde tracers in order to determine the degree of collateralization between these pathways. Approximately 20% of retrogradely labelled neurons displayed both tracers, indicating that collateralization and damage to fibres of passage could not account for all of those cases in which D1 agonist-induced Fos-like immunoreactivity was detected in accumbal neurons projecting to the ventral pallidum.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural study of CCK and tyrosine hydroxylase immunoreactivity in the rat nucleus accumbens.

The cholecystokinin (CCK)- and tyrosine hydroxylase (TH)-like immunoreactive (LI) axons and boutons were studied in the caudal and medial parts of the rat nucleus accumbens (NAC), using the indirect immunoperoxidase technique, at the electron microscopic level. Both CCK- and TH-LI boutons contained clear synaptic vesicles and large granular vesicles of similar size, but the CCK-LI boutons contained more large granular vesicles than TH-LI boutons. The CCK-LI and TH-LI boutons were heterogeneous. This finding might be related to the various immunoreactive neuronal types innervating the caudomedial NAC. However, the CCK-LI boutons (containing mostly small, round, clear synaptic vesicles) formed mainly asymmetrical synaptic contacts with dendritic spines whereas the TH-LI boutons (containing medium-sized as well as small, round, clear synaptic vesicles) formed mostly symmetrical synaptic contacts with dendritic shafts.

The effect of clozapine on Fos protein immunoreactivity in the rat forebrain is not mimicked by the addition of alpha 1-adrenergic or 5HT2 receptor blockade to haloperidol.

The involvement of alpha 1-adrenergic and 5HT2-receptor blockade in the induction of Fos protein produced by the 'atypical' neuroleptic clozapine was investigated in the rat forebrain. The Fos protein immunohistochemical technique has been used to identify the anatomical substrate underlying the effects of typical and atypical neuroleptics. Clozapine (20 mg/kg) induced a significantly higher Fos protein immunoreactivity response in the medial prefrontal cortex and a significantly lower response in the dorsolateral striatum compared to the effect of haloperidol (1 mg/kg). The alpha 1-adrenergic antagonist prazosin (0.3 and 1.0 mg/kg) and the 5HT2 antagonist ritanserin (1 and 3 mg/kg) did not increase Fos protein immunoreactivity by themselves and did not mimic the clozapine response when co-administered with haloperidol (1 mg/kg). Consequently, this study suggests that neither alpha 1-adrenergic receptor blockade nor the 5HT2-receptor blockade accounts for the unique Fos protein expression pattern produced by clozapine.

Clozapine decreases neuropeptide Y-like immunoreactivity and neuropeptide Y mRNA levels in rat nucleus accumbens.

The aim of this study was to evaluate the effect of acute, subchronic (14 days) and chronic (28 days) intraperitoneal (i.p.) administration of clozapine (10 or 25 mg/kg) on neuropeptide Y (NPY) system activity in the nucleus accumbens of the rat. NPY-like immunoreactivity (NPY-LI) decreased 24 h after subchronic clozapine while NPY mRNA after both acute and subchronic clozapine treatment. NPY-LI levels were also reduced 8 days after cessation of chronic lower-dose treatment. Subchronic (14 days) administration of the 5-HT2A antagonist ketanserin (1 mg/kg i.p.) or the dopamine D2/D3 antagonist (+/-) sulpiride (100 mg/kg i.p.) reduced NPY-LI levels, whereas the dopamine D1-like antagonist SCH 23390 (0.5 mg/kg i.p.), dopamine D4 antagonist L-745,870 (1 mg/kg per os), and alpha1-adrenergic antagonist prazosin (0.2 mg/kg i.p.) had no effect. There were no significant differences between the ketanserin-induced decrease in NPY-LI levels and the effects of the following two-drug combinations: ketanserin and SCH 23390, ketanserin and L-745,870, and ketanserin and prazosin. The study has shown that clozapine reduces NPY system activity in the rat nucleus accumbens. It seems that the action of clozapine is partly mediated by blockade of 5-HT2A and D2/D3 dopaminergic receptors.

Attenuation of cocaine-induced conditioned place preference by Polygala tenuifolia root extract.

A recent investigation indicated that Polygala tenuifolia Willdenow extract (PTE) possesses a potential antipsychotic effect. In this study, we examined the effects of PTE on the cocaine-induced changes in locomotor activity, conditioned place preference (CPP), fos-related antigen-immunoreactivity (FRA-IR), and activator protein (AP)-1 DNA binding activity. Cocaine-induced behavioral effects (hyperlocomotion and CPP) occurred in parallel with increases in FRA-IR and AP-1 DNA binding activity in the nucleus accumbens. These responses induced by cocaine were consistently attenuated by concurrent treatment with PTE (25 mg or 50 mg/kg/day, i.p. x 7). The adenosine A2A receptor antagonist, 1,3,7-trimethyl-8-(3-chlorostyrl)xanthine (0.5 or 1.0 mg/kg, i.p.), reversed the PTE-mediated pharmacological action in a dose related manner; neither the adenosine A(1) receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine (0.5 or 1.0 mg/kg, i.p.) nor the A2B receptor antagonist, alloxazine (1.5 or 3.0 mg/kg, i.p.) significantly affected this pharmacological action. Our results suggest that PTE prevents cocaine-induced behavioral effects, at least in part, via the activation of the adenosine A2A receptor.

Involvement of the nucleus accumbens in stimulation of the immune response in rats after activation of opioid mu receptors with DAGO.

The involvement of the nucleus accumbens in neuroimmunostimulation was demonstrated during activation of opioid mu receptors with the selective agonist DAGO (100 microg/kg); single doses of this agent to sham-operated (control) Wistar rats induced significant increases in the numbers of direct IgM antibody-forming and total rosette-forming cells after immunization with sheep erythrocytes. Bilateral electrolytic lesioning of the nucleus accumbens in rats led to sharp decreases in the intensity of immune responses; there was no immunostimulation after administration of DAGO to these animals. These data provide evidence for the involvement of the nucleus accumbens in the process of immunomodulation and for the importance of opioid mu receptors in the nucleus accumbens in the stimulation of immunogenesis.